A dual-type wireless communication terminal capable of performing communication with base stations with switching between two communication systems has been known.
Patent Document 1: JP-A-H9-172675
Out of the above dual-type wireless communication terminals, a wireless communication terminal, which can measure a wireless communication status of one communication method during communication using another communication method and monitor an incoming call, is especially called a hybrid type.
In relation to the hybrid-type wireless communication terminal, a hybrid-type wireless communication terminal using a cdma2000 1x system which is mainly designed for voice communication and a 1xEVDO system which is specifically designed for data communication monitors the status of radio wave of each system and an incoming call from the base station by means of switching an antenna and a radio section to each system at predetermined intervals.
The interval used for the system monitoring is specified by each system, and the wireless communication terminal controls timing in cooperation with the base station so as to prevent occurrence of an overlap between monitoring of the cdma2000 1x system and monitoring of the 1xEVDO system (see FIG. 2).
While system monitoring is performed under with one system, monitoring with another system cannot be performed because the antenna and the radio section are occupied.
Here, when the base station under monitoring has changed as a result of that idle handoff (handoff arising in an idle state) has arisen in the cdma2000 1x system by deterioration of the radio wave status, the timing of system monitoring may change.
In this case, the timing of monitoring the 1xEVDO system must be changed such that an overlap does not arise between the timings of monitoring the two systems.
At this time, since the 1xEVDO system carries out communication with the base station in order to change the monitoring timing, the antenna and the radio section are occupied by the 1xEVDO system.
Incidentally, in the 1xEVDO system, the wireless communication terminal awaits in a measurement status where an incoming signal output from the base station can be received during a certain period of time after completion of communication processing with the base station, in consideration of occurrence of disconnection due to instantaneous interruption of a radio wave during communication.
For this reason, the antenna and the radio section are occupied by the 1xEVDO system for a certain period of time after termination of communication.
Therefore, the cdma2000 1x system cannot detect an incoming call while the 1xEVDO system performs processing in order to change the timing of the system monitoring, as well as during a subsequent certain period of time.
Particularly, when the cdma2000 1x system is in an area where idle handoff arises frequently; i.e., where a conflict occurs between the signals output from a plurality of base stations, the idle handoff frequently arises after the processing for changing the timing of monitoring the 1xEVDO system after the idle handoff of the cdma2000 1x. Therefore, the incoming call arrival rate of the cdma2000 1x drops extremely.